1. Field of the Invention
The present invention relates to curable resinous compositions, which contain an inorganic filler which has been surface-treated with an organophosphorus compound. The present curable resinous compositions may be used as materials for industrial use and as a biological hard tissue materials. As examples of such materials, there may be mentioned molding compositions, composite resins for dental use (filling and restoration materials, materials for making inlays, artificial crowns, artificial tooth, abutment construction materials), dental adhesives, denture base materials, impression materials, artificial bones and bone cements.
2. Discussion of the Background
The term "curable resinous composition" as used herein means a composition containing, as essential components, an inorganic filler and a polymerizable monomer.
Recently, in the field of dental care, compositions containing an inorganic filler and a polymerizable monomer, for example, composite resins for dental use, have come into use. The inorganic fillers used in composite resins for dental use are generally subjected to preliminary surface treatment. The surface treatment improves the wettability at the filler-polymerizable monomer interface, makes it possible to increase the filler content, and improves the dispersibility of the filler in the composition. As a result, composite resin moldings obtained by polymerization of the monomer have improved mechanical strength owing to good adhesion at the filler-resin interface. Known in the art as surface treating agents for such purposes are silane coupling agents, typically .gamma.-methacryloyloxypropyltrimethoxysilane.
More broadly, in the industrial field, there are known, as other surface treating agents for inorganic fillers, titanate coupling agents, zircoaluminate type coupling agents, higher alkyl alcohols, higher fatty acids, organophosphate esters, and so forth. Among them, the organophosphate esters are related to the present invention and therefore are summarized below.
Japanese Patent Publication No. 60-3431 discloses inorganic fillers surface-treated with organophosphate esters of the formula: ##STR2## wherein R.sub.1 is a hydrogen atom or a methyl group and R.sub.2 is an alkylene group containing 2 to 6 carbon atoms or a halogen-substituted derivative thereof, a polyoxyethylene group of the following formula: EQU --CH.sub.2 --CH.sub.2 --(O--CH.sub.2 --CH.sub.2).sub.n -- (n=1 to 20)
or a polyoxypropylene group of the following formula: ##STR3##
Japanese Laid-open Patent Application Kokai No. 59-170131 discloses inorganic powders surface-treated with one or more organophosphorus compounds of the general formula: ##STR4## wherein R and R' are the same or different and each is an alkyl, alkenyl, aryl, alkoxy, alkenoxy or aryloxy group containing 1 to 30 carbon atoms or a group derived from these organic groups by substitution.
In addition, Japanese Laid-open Patent Applications Kokai Nos. 56-54795, 57-128728, 57-168954, and 57-198735, describe similar technical ideas.
These known resinous compositions for industrial use comprise a polymer and a surface-treated inorganic filler. Since the polymer has no or few reactive groups, the possibility that the polymer may be bound chemically to the surface-treating agent to a high degree is small and therefore only limited improvements in mechanical properties are attained. Accordingly, resinous compositions in which the resin is bound to the surface-treating agent to a high degree and which can give good mechanical properties are highly desirable.
Furthermore, compositions for dental use, to which an aspect of the present invention is directed, are required to possess water resistance, which is a very important property since the cured moldings from said compositions may be used in the oral cavity for a prolonged period of time. Accordingly, resinous compositions of good water resistance are also desired.
The above-cited prior art references are not concerned with improving the water resistance of the respective resinous compositions or of the applicability of the compositions in dentistry. Thus, it is impossible to anticipate from said references that the known organophosphorus compounds might be effective in achieving the objects of the present invention.
Inorganic fillers in conventional resinous compositions, especially those in dental use, mostly have a high silicon content (for example, silica and silica-based glasses). Only in very rare cases, have inorganic fillers containing a metal or a metal oxide or salt as a main constituent, been put to practical use in resinous compositions.
As the main reason why such metal element-containing inorganic fillers have not been used in resinous compositions, there may be mentioned the fact that the technology of surface treatment of said fillers has not been established. The surface treatment effect of known silane- or titanium-containing surface-treating agents, on these inorganic fillers, is not so remarkable as those on silica. Therefore, resinous compositions containing large amounts of these fillers treated with known surface treating agents suffer from disadvantages such as decreased strength (in particular under wet conditions) or dislodgement of the filler due to insufficient bonding at the resin-inorganic filler interface.
However, it might be expected that the use of a metal, metal oxide or metal salt as an inorganic filler might give resinous compositions possessing more favorable characteristics as compared with the conventional silica-containing compositions.
For instance, replacement of silica with a metal oxide such as alumina or zirconia might give composite resins for dental use which have an aesthetic appearance, good mechanical strength, and good chemical stability, and incorporation of a filler close in composition to a natural tooth, such as hydroxyapatite, might provide dental adhesives having good biocompatibility. The use of a metal filler could make it possible to develop new types of composites for dental use which have ductility and toughness.
In view of the foregoing, the possibility of a surface treatment technology effectively applicable to the above-mentioned metal element-containing inorganic fillers has been investigated.